Soon after the Louisiana Purchase, which transferred control of Missouri's land from the French to the U.S., Congress created the Missouri Territory in 1805. The territory would go on to become the 24th state in the Union, following a process set up by the Northwest Ordinance of 1787.

Drafted and accepted while the United States were under the Articles of Confederation, the Northwest Ordinance of 1787 set up a procedure by which territorial properties could become full-fledged states, equal to the original 13. The Ordinance held that prospective states must go through three stages of representation in government, advancing as the territorial population increases. It also prohibited slavery in the Northwest Territory (the region between the Ohio and Mississippi rivers), a provision that would complicate the admission of Missouri into the Union.

In 1805 Missouri became a first-class territory. Under the Northwest Ordinance, this meant that the government of Missouri would consist primarily of a governor, a secretary, and three judges. All five of these positions were to be appointed by the President; the territorial citizens did not get to vote. Thomas Jefferson chose James Wilkinson as governor, a highly controversial appointment. Suspicion about Wilkinson's loyalties led to political division in Missouri, and eventually resulted in his ouster in 1806. Secretary Frederick Bates and Indian affair superintendent William Clark served as acting governors until Jefferson's replacement appointee, Meriwether Lewis, arrived in 1808. In the midst of this confusion, the population of Missouri increased rapidly, further complicating some aspects of government, especially land title recognition.

This larger population, over 20,000, led to the recognition of Missouri as a second-class territory in 1812. As a second-class territory, Missouri citizens got the right to vote for their representatives in the lower house of the territorial legislature (the President appointed the upper house's members) and for a nonvoting representative in the U.S. House of Representatives. Second-class status also meant that municipalities could collect taxes and administer the day-to-day affairs of the growing areas. Missouri's population continued to increase – the mining and fur trading industries drew settlers, as did the fact that Missourians could legally own slaves.

Missouri became a third-class territory in 1816, meaning that its citizens could elect both houses of their territorial legislature. In 1818 the first petition for recognition of Missouri as a state was introduced in the U.S. House of Representatives by Missouri's delegate, John Scott. In 1819, Representative James Tallmadge complicated the proceedings, calling for an end to slavery in Missouri. Tension rose between slavery and anti-slavery forces, since at the time, there were an equal number of slave and free states – neither side wanted the other to have a majority.

The first Missouri Compromise helped clear the power-balance obstacle. Congressmen Henry Clay and Jesse Thompson orchestrated the agreement that would allow Maine to become a state at the same time as Missouri. Under the Compromise, Maine was to be admitted as a free state and Missouri was allowed to enter as a slave state. The Compromise further held that slavery would be prohibited in all other areas of the Louisiana purchase north of Missouri's southern border.

Following the Missouri Compromise, Missouri moved to draft a constitution. Slavery remained a polarizing issue – the Constitutional Convention's finished product was seen as conflicting with the U.S. Constitution in its prohibition of free blacks from emigrating to the State. Although Missouri had already held elections for state offices and selected a (temporary) state capital in 1820, it was not until mid-1821 that Missouri was officially admitted into the Union. Under Henry Clay's “Second Missouri Compromise,” Missouri's legislature had to pass a resolution promising not to enforce its state Constitution's “questionable” provisions. The first governor of Missouri,  Alexander McNair, called for the legislature to make this resolution.

Missouri's state government complied, albeit reluctantly and not forcefully, and by President Monroe's proclamation formally made Missouri one of the United States. The strife that preceded its statehood foreshadowed upcoming conflicts – the Missouri Compromise is seen as one of the major cause of tensions that led to the Civil War. In spite of the conflicts, Missouri became the 24th state on August 21, 1821.

1. New Madrid earthquake
   The New Madrid earthquake of 1811 was one of the largest earthquakes to ever hit the United States; its tremors were felt thousands of miles away. The town of New Madrid sits near the tectonic fault where the quake originated. The damage from the quake shook settlers confidence in the safety of the area, and eventually Congress offered to replace damaged property. The program was plagued by fraud; even the governor of Missouri was  implicated in a speculation scheme.
2. Meriwether Lewis and William Clark
   Meriwether Lewis and William Clark were the heads of the “Corps of Discovery,” which explored the newly-acquired Louisiana Territory for President Thomas Jefferson in 1804. They made and recorded numerous discoveries about the land, flora, fauna, and natives, providing the period's best description of the area. Both Lewis and Clark served as territorial governors of Missouri after the expedition (Clark as acting governor).
3. Frederick Bates
   Fredrick Bates served as acting governor of the Missouri territory starting in 1807. His official position, territorial secretary, required him to review land claims following the transfer of the Louisiana territory to the French by the Spanish and to the U.S. by the French. Congress initially started the review of land claims to ensure fraudulent claims were not honored. After approving just over 1/3rd of the claims, Congress left the task to territorial governments. Bates continued the approval of genuine claims and rejection of illegitimate ones for four years.
4. Thomas Hart Benton
   Thomas Hart Benton was a controversial politician in the 19th century. He started out as a lawyer and the editor of the St. Louis Enquirer, and then was elected by the new Missouri Congress as one of Missouri's first U.S. senators.  As a senator, he was a polarizing figure, supporting a “hard money” economy and writing editorials on slavery restrictions.
5. Henry Clay
   Henry Clay was a Kentucky politician known for his role in the passage of the two “Missouri Compromises.” As the Speaker of the House in 1819, he helped orchestrate the terms under which Missouri and Maine would be admitted as American states. Later, he made it so that Missouri must not pass legislation (regarding free black immigration) contrary to the U.S. Constitution in order to be admitted into the union.
6. Alexander McNair
   Alexander McNair was the first governor of the state of Missouri. Elected in 1820, he easily beat his opponent William Clark by campaigning extensively in Missouri. As governor, he called for the new state congress to convene to comply with the provisions of the “Second Missouri Compromise.” He was also one of the delegates to Missouri Constitutional Convention.
7. General James Wilkinson
   James Wilkinson was a controversial governor of territorial Missouri in the early 19th century. Suspected of counter-revolutionary dealings with Aaron Burr and espionage with the Spanish government, his governorship divided the territory. He remained a controversial figure as governor, listening to French special interests and refusing to meet with other officials. He was eventually replaced be Meriwether Lewis as governor.
8. Pierre Chouteau
   Pierre Choteau was a prominent fur trader in Missouri. The brother of a co-founder of St. Louis, Choteau monopolized the fur trade there from 1794 to 1802. Later, he was a co-organizer of the Missouri Fur Company, a prominent pelt trading entity that lasted until 1813. His dealings emphasized the importance of St. Louis as a trading center, helping establish it as one of the most active and populated regions in the state.
9. Franklin, Missouri
   Franklin, Missouri was one of the largest settlements in the territory/ state in the early 19th century. Established in 1817, it was home to a population boom. It was known for its businesses (including newspapers), federal land office, and well-developed land. Its large size made it one of the few towns in Missouri to contain both a library and a coeducational school.
10. Fort Osage
    Fort Osage was a fort built on the Missouri River on land formerly owned by the Osage Indian tribe. Superintendent of Indian affairs William Clark and the leaders of the Osage agreed to a treaty in 1808 that would give Missouri control of the land on which the fort was built. In exchange, the Osage were promised that Missouri would establish a trading post and pay the tribe a yearly fee.